This invention relates to golf balls, and more particularly, to a golf ball made of an improved rubber composition.
Conventional golf balls are made by molding a cover about a core (typically 11/2" diameter core). The core is either a solid core, solid mass of material, or a wound core, elastic thread wound about the center. The center may be either a solid mass of material or a liquid filled cavity which is frozen prior to winding. Golf balls with solid cores are generally referred to as "two piece" golf balls while golf balls with wound cores are generally referred to as "three piece" golf balls. One piece golf balls are made from a homogeneous mass of material.
Rubber compositions now used as cores for two piece golf balls are formulated to possess high hardness and high compressive strengths. With such a formulation, the resiliency to optimize flight distance performance can be achieved. "Click" and "feel" are other qualities sought from a golf ball. "Click" is the sound made by a golf club head when it hits the ball. "Feel" is the overall sensation transmitted to the golfer after hitting the ball.
The polybutadiene elastomer commonly used for the rubber component of a core is crosslinked by a large amount of a zinc salt of acrylic or methacrylic acid, in order to increase hardness without decreasing resilience. Golf ball compounds crosslinked by acrylic acid zinc salts have generally exhibited superior characteristics in terms of resilience but tend to be less durable. Ball forming compounds crosslinked by methacrylic acid zinc salts produce a ball of superior durability but at the expense of resilience.
To date, golf ball manufacturers have added fatty acids to the golf ball to obtain the desired resiliency and compressive strengths. For example, Tominaga et al, U.S. Pat. No. 4,561,657, teaches that an improved golf ball can be made from a rubber composition containing zinc acrylate coated with a fatty acid such as stearic acid whereby the golf ball exhibits proper hardness, good impact resilience-and good sound and feel when hit. Another characteristic of this type of rubber composition is that it creates good roll workability and dispersability of rubber additives.
It is desirable, however, to obtain a golf ball with a softer feel, and desirable click with excellent flight and distance performances while maintaining resilience and getting a designed reduction of hardness and compressive strengths.